在Django中更新一對多參考字段也會更新其他對象

Question

我有一個現有的帶有兩個表的數據庫，名爲Identities和Accounts，我試圖使用Django ORM進行管理。

身份與賬戶一個一對多的關係，我模仿了兩個表是這樣的：

class Identity(models.Model): 
    class Meta: 
     managed = False 
     db_table = "Identities" 
    i_id = models.AutoField(db_column = "I_ID", primary_key = True) 
    name = models.CharField(db_column = "DisplayName", max_length = 200) 

class Account(models.Model): 
    class Meta: 
     managed = False 
     db_table = "Accounts" 
    name = models.CharField(db_column = "Name", max_length = 200, primary_key = True) 
    identity = models.ForeignKey("Identity", db_column = "I_ID", blank = True, null = True, related_name = "accounts") 

我的問題是，當我更新相關聯的賬戶身份，相關聯的所有帳戶新的標識將切換到新的一個：

old_identity = Identity.objects.create(name = "Old") 
new_identity = Identity.objects.create(name = "New") 
account_1 = Account.objects.create(name = "account_1", identity = old_identity) 
account_2 = Account.objects.create(name = "account_2", identity = old_identity) 

# change the identity for account_1: 
account_1.identity = new_identity 
account_1.save() 

# read account_2 from DB and check identity 
account_2 = Account.objects.get(name = "account_2") 

# identity is now "New" also for account_2! 
print account_2.identity.name 

如果我直接在數據庫中做同樣的更新，只有我更改帳戶的身份變了，沒有關聯身份的所有帳戶，所以這是由Django引入的。

我應該怎樣才能在更改identity字段時更新一個帳戶？

注意：只是要清楚，這兩個引用也在數據庫中更改，這不是數據未刷新或類似的問題。

Answer 1

從已發佈的相關代碼中檢查問題。發佈代碼運行正常：

創建表：

(venv)dani@egg-v3:~/tmp/lldldl/paolo$ python manage.py migrate 
Operations to perform: 
    Synchronize unmigrated apps: mytest 
    Apply all migrations: admin, contenttypes, auth, sessions 
Synchronizing apps without migrations: 
    Creating tables... 
    Creating table mytest_identity 
    Creating table mytest_account 
    Installing custom SQL... 
    Installing indexes... 
Running migrations: 
    Applying contenttypes.0001_initial... OK 
    Applying auth.0001_initial... OK 
    Applying admin.0001_initial... OK 
    Applying sessions.0001_initial... OK 

運行：

(venv)dani@egg-v3:~/tmp/lldldl/paolo$ python manage.py shell 
Python 2.7.3 (default, Feb 27 2014, 19:58:35) 
[GCC 4.6.3] on linux2 
Type "help", "copyright", "credits" or "license" for more information. 
(InteractiveConsole) 
>>> from mytest.models import Account,Identity 
>>> old_identity = Identity.objects.create(name = "Old") 
>>> new_identity = Identity.objects.create(name = "New") 
>>> account_1 = Account.objects.create(name = "account_1", 
             identity = old_identity) 
>>> account_2 = Account.objects.create(name = "account_2", 
             identity = old_identity) 
>>> 
>>> # change the identity for account_1: 
>>> account_1.identity = new_identity 
>>> account_1.save() 
>>> 
>>> # read account_2 from DB and check identity 
>>> account_2 = Account.objects.get(name = "account_2") 
>>> 
>>> # identity is now "New" also for account_2! 
>>> print account_2.identity.name 
Old 
>>> 

測試使用Django 1.7和sqlite3的。也許一些數據庫觸發器？ Post/Pre保存信號？